The present disclosure generally relates to eye tracking in a head-mounted display (HMD), and specifically to using an infrared transparent backlight device for eye tracking applications in a HMD.
HMDs are becoming increasingly compact and have a higher field of view. As a result, there are increasing constraints on space available for eye tracking systems. Additionally, some applications expand the field of view requirements to also scan facial features, which further complicates the placement of tracking optics.
Conventional spatial light modulators are typically backlit, and the backlight may include an OLED emissive panel, a collimation system using one or more emissive elements with one or more refractive or reflective elements, or both, or a light guide system. Such backlight assemblies are opaque and scatter infrared (IR) light, and will not allow viewing a user's eye through the backside of the display module. For example, an IR camera positioned to image an object through a backlight assembly would have poor image quality due to the scattering of IR light caused by the backlight assembly.